Apparatus for eliminating interferences in radio reception



3, 3 P. L. v. LAMBERT 1,980,212

APPARATUS FOR ELIMINATING INTERFERENGES IN RADIO RECEPTION Filed May 23, 1933 wilrwssesx Patented Nov. 13, 1934 ice,

APPARATUS FOR 'ELIMINATING IN TER- FERENCES IN RADIO RECEPTION Pierre :Louis Victor Lambert,

St. Martins,

Guernsey, Channel Islands, assignor of twofifths to Harold Hickman Randell, Guernsey,

Channel Islands Application May 23, 1933, Serial No. 672,423

' In Great Britain May .26, 1932 I TClaims. (crzao -z o) This invention has reference to wireless (radio) receiving apparatus and relates to circuit arrangements to be'connected to or incorporated in such apparatus for the purpose of eliminating the eifect of radio-frequency interferences induced in the aerial circuit of the receiver by electric conductors used in feeding the receiver, particularly the power and light mains or lines; the object being to eliminate the effects of interfering currents in the primary oscillatory circuit of the receiver by the employment of means adapted to render equal the respective potential differences toearth on the aerial and earth sides of the said circuit due to the interfering currents and independently of the frequency of the said currents.

To this end, the circuit arrangements comprise:(a) a means to establish or vary the mutual inductance and capacitance coupling, M,

9 between the aerial circuit and the electric lines carrying the interfering currents; (b) a means to establish or vary, for the interfering currents,-

of an inductance of definite impedance to the in-' terfering currents, through whichinductance' the current from the mains used for feeding the receiver passes and, in parallel with such inductance, a fixed or variable condenser in series with a fixed or variable resistance, whereby the amplitude and phase-angle of the interfering currents in the said parallel circuit so formed are adapted for regulation.

The varying referred to under (a) which may be dispensed with if certain conditions are met naturally, is obtained by placing a variable electric coupling between the aerial lead-in and a point (P) on the mains side of the circuit referred to in (b), such point being formed by placing (in series) across the mains lead a condenser of such capacity as will bring the'mains leads at that point at an equal'electrical high frequency difference of potential to earth. The

coupling (a) combines with the filter (b) in such a manner as to make equal the phase-angle and amplitude of the interfering potential differences to earth on each side of the primary oscillatory circuit of the receiver for all frequencies whereof the corresponding impedance of the primary circuit is not negligible.

'Under certain conditions of earthing of the mains, it will be necessary to place, on the mains side of the above mentioned point (P) on one or both mains leads, a circuit similar to that hereinbefore described as (b) to regulate the high frequency resistance between'the point (P) and the earth. i I

'In the accompanying drawing:--

Figure 1 is a diagrammatic representation of the circuit arrangement of which the function is similar to that of a Wheatstone bridge.

Figure 2 is a diagrammatic representation of thegpractical realization of the circuit arrangement applied to an all-mains Wireless receiver, there being a variable impedance on the lead 70 consisting of a variable inductance and condenser in parallel and a variable resistance and condenser in series.

Figure 3 is another diagrammatic representation of the practical realization of the circuit arrangement having similar characteristics to that of Figure 2 and showing a variable impedance consisting of a variable condenser and inductance'in parallel and a lead to earth through a condenser and earth resistance Referring first to Figures 2 and 31- Let-it be assumed thatX, X indicates a portion of a distributing main (with one side earthed, say X) feeding the receiver Z. It is required that 85 the unwanted electric waves or transients carried along X, X should not interfere with the ultimate purpose of the receiver by their electrokineticieffect or by the electrostatic field they create or by the electromagnetic waves due to them which may be induced into the aerial system of thereceiver Z through the mutual inductance and capacity coupling mainly due to the inductances and capacities K K K existing naturally between the aerial, the mains X, X and the earth (a natural direct coupling between X, X

and aerial is not represented in the drawing) or D generally placed in the negative lead is a variable impedance consisting of (a) an inductance, or

(b) a low frequency choke, the inductance of which will depend upon the amount and frequency of hum to be eliminated, or

(c) a combination of (a) and (b), and

(d) a variable resistance R and condenser in series arranged in parallel with (a) or/and (b) The current feeding the receiver will pass through (i) or (ii) of Z and through (a) (b) or (c) of D.

L, L are leading impedances preceding the bridge either or both ofv which may be used and which may be composed of pure inductances or either or both of such connections to obtain a required value of resistance.

At T, R represents the value of, the impedance between the device and the earth; this earth connection is the only one required for the receiver and the device and can be made on either branch in a or a.

R represents the value of the impedance between the electric lines and the earth; this im-,

pedance may be increased by L or decreased by making a better earth connection at a suitable point of the line to regulate the voltage V across the bridge created by the interfering currents (Figure 1).

C represents a condenser placed across the mains leads at points taken on the mains side of Z and D to bring such points of the leads at an equal high frequency difference of potential to earth (thus determining the electric point P) (Figure 1).

C represents a condenser placed across the mains leads on the receiver side of Z and D.

C represents a condenser in series between the earth connection and a point taken between Z or D and the oscillatory circuit of the receiver.

The condenser indicated at K K, K in Figure 1 is not representative of the capacity value existing between aerial and earth; this value is represented by K in Figures 2 and 3, but it implies that K ,'K K combine, together with acertain inductance and capacitance existing between aerial and mains (not represented in the drawsing), to form the induced Voltage V (Figures .2 and 3) between aerial and earth.

The voltage V across the bridge is considered as if the inductances L, L were short circuited;

' There is no resistance introduced in the oscillatory circuit of the set, a direct connection to earthbeing obtained in the arrangement shown in Figures 2 and 3 through b, a, C, a, C R any resistance to this oscillatory circuit which might be placed in the set should be shunted by a condenser of suflicient capacity. Such a case would occur if the device were placed on the mains side of the transformer when the mains of the mains carrying direct current or if the de-- vice is placed after the rectifier.

A circuit such as Z or D may replace the impedance found on the positive side of an allmains wireless receiver between a and the oathode-heating circuit (Figs. 2 and 3).

On the negative side there must be no impedance between a and the aerial oscillatory circuit; D will be in series with the negative lead on the mains side of a.

In the case of a set getting only its anode current from the mains it will be necessary to connect the points a and a to the filament (for instance to the cathode-heating battery) through condensers of sufficient capacity and to the anode current-supplying unit in the ordinary way.

Referring now to Figure 1--in reality a diagrammatic representation of Figures 2 and 3 showing that the function thereof is similar to that of a'Wheatstone bridge, the interfering currents carried along the distributing main X, X create a voltage (V) across the diagonal XT of the bridge, while the oscillatory circuit of receiver Z to be protected therefrom is operable across the other diagonal of the bridge (viz: that wherein the galvanometer is normally placed).

The natural couplings between aerial and and the other end of the. same diagonal, the

equilibrium of the bridge will be obtained when V+V =V and when the phase-angle of (V +V equals the phase-angle of V The equilibrium so obtained is maintained by the correct adjustment of the device for a range of frequencies depending upon the frequency at which the primary oscillatory circuit of the receiver is tuned.

The correct adjustment of the variable impedances of (D, Z) and K will givev this equilibrium (D, Z) being one impedance (to the interfering currents) composed of D and Z in parallel.

In some cases the natural value of coupling (that is the capacity existing naturally between aerial, lead-in and earth) may satisfy the desired relation between the quantities K R K.

(Z D) thus indicating a form of the invention in which the variable condenser K may be dispensed with.

The valuesof the components used in the circuits herein described may be computed from the following figures:

The h. f. inductances of Z, L and L may vary between 0 and 4000 microhenries.

The resistance of R and R may vary between 0 and 5000 ohms.

The capacity of the condensers in series with R and R may vary between 0.001 and 2 microfarads.

The capacity of K may vary between 0 and .0005 microfarads.

The capacity of the condensers C and C may vary in mic'rofarads up to 20 microfarads and that of the condenser C up to infinity.

The complete device may be placed in or near the receiver or at a distance from it.

I claimu- 1. In wireless receiving apparatus, for eliminating the effect of radio-frequency interferences induced in the aerial circuit by electric lines used in feeding the receiver, a device which consists of circuit arrangement-s comprising a filter com posed of two inductances through which the current feeding the receiver is passed and whereof one is placed in series ineach lead of the distributing mains, there being placed on each'side of said inductances in series across the mainsleads a condenser to bring the mains leads at these 7 points an equal electric high frequency difference of potential to earthancl, in parallel with the said inductances a variable condenser in series with a variable resistance, the said filter being interposed at a point between the mains leadsand the receiver and the mains side of the filter being electrically coupled by means of a variable condenser and a variable resistance in series to one point of the aerial lead-in while the receiver side of the filter is earthed, all impedances between this earthing point and the earth cathode side of the primary oscillatory circuit of the reeiver being shunted by condensers.

Z. In wireless receiving apparatus for eliminating the effect of radio-frequency interferences induced in the aerial circuit by electric lines used in feeding the receiver, a device which consists of circuit arrangements comprising a filter composed of a fixed inductance of high impedance to the interfering currents in series in one of the mains leads while in the other mains lead there is a variable inductance, there being placed on each side of the said inductances and in series across the mains leads a condenser to bring the mains leads at these points at an equal electric high frequency difference of potential to earth and placed in parallel with the said inductances a variable condenser in series with a variable resistance, the said filter being interposed at a point between the mains leads and the receiver and the mains side of the filter being electrically coupled by means of a variable condenser and a variable resistance in series to one point of the aerial lead-in while the receiver side of the filter is earthed, all impedances between this earthing point and the earth-cathode side of the primary oscillatory circuit of the receiver being shunted by condensers.

3. In wireless receiving apparatus for eliminating the effect of radio-frequency interferences induced in the aerial circuit by electric lines used in feeding the receiver, a device which consists of circuit arrangements comprising a filter composed of two inductances through which the'current feeding the receiver is passed and whereof one is placed in series in each lead of the distributing mains, there being, in parallel with the said inductances, a variable condenser in series with a variable resistance, and there being placed on the receiver side of the said inductances and in series across the mains leads a condenser to bring the mains leads at these points at an equal electric high frequency difference of potential to earth while on the mains side of the said inductances there is placed in series across the mains leads a condenser in series with a variable resistance, the said filter being interposed at a point-between the mains leads and the receiver and the mains side of the filter being electrically coupled by means of a variable condenser and a variable resistance in series to one point of the aerial leadin while the receiver side of the filter is earthed, all impedances between this earthing point and the earth-cathode side of the primary oscillatory circuit of the receiver being shunted by condensers.

4; In wireless receiving'apparatus-for elimin'ating the effect of radio-frequency interferences in- 'duced intheaerial circuit by electric'lines used in feeding the receiver, a'device which consists of circuit arrangements-comprising a filter composed of 'a fixed inductance of high impedance to the interfering currents in series in one of the mains leads while in the'other mains lead there is a variableinductance there being placed in parallel'withthesaidinductances a variable condenser in series with a variable resistance, the said filter being interposed at a point between the mains leads and the receiver and the mains side of the filter being electrically coupled by means of a variable condenser and a variable resistance in series to one point of the aerial lead-in while the receiver side of the filter is earthed, all impedances between this earthing point and the earth cathode side of the primary oscillatory circuit of the receiver being shunted by condensers.

5. In wireless receiving apparatus for eliminating the effect of radio-frequency interferences induced in the aerial circuit by electric lines used in feeding the receiver, a device which consists of circuit arrangements comprising a filter composed of a pair of inductances through which the current feeding the receiver passes and whereof one is placed in series in each lead of the distributing mains, there being placed on each side of the said inductances in series across the mains leads a condenser to bring the mains leads at these points at an equal electric high frequency difference of potential to earth and in parallel with the said inductances a variable condenser in series with a variable resistance, the filter being interposed at a point between the mains leads and the receiver and the mains side of the filter being electrically coupled by means of a va riable condenser and a variable resistance in series to one point of the aerial lead-in while the receiver side of the filter is earthed and the electric continuity is established between the earthing point of the filter and the earth-cathode side of the primary oscillatory circuit of the receiver by means of a condenser, impedances between the earthing point of the filter and the earth-cathode side of the primary oscillatory circuit being shunted by condensers.

6. In wireless receiving apparatus for eliminating the effect of radio-frequency interferences induced in the aerial circuit by electric lines used in feeding the receiver, a device which consists of circuit arrangements comprising a filter composed of two inductances through which the current feeding the receiver passes and whereof one is placed in series in each lead of the distributing mains there being a low frequency choke in series with the inductance on one side of the filter and on each side of the said inductances in series across the mains leads a condenser to bring the mains at these points at an equal electric high frequency difference of potential to earth and, in parallel with the said inductances, a variable condenser in series with a variable resistance, the filter being interposed at. a point between the mains leads and the receiver and the mains side of the filter being electrically coupled by means of a variable condenser and a variable resistance in series to one point of the aerial lead-in while the receiver side of the filter is earthed, all impedances between this earthing point and the earth-cathode side of the primary oscillatory circuit of the receiver being shunted by condensers.

7. In wireless receiving apparatus for eliminating the effect of radio-frequency interferences induced in the aerial circuit by electric lines used in feeding the receiver when such receiver is fed through a transformer, a device which consists of circuit arrangements comprising a filter composed of two inductances through which the current feeding the receiver passes and whereof one is placed in series in each lead of the distributing mains, there beingincluded in series with the inductance on one side of the filter a low-frequency choke and the electric coupling being established between the lead-in and the electric mains at a point in the latter. preceding the transformer, also placed on each side of the said inductances in series across the mains leads a condenser to bring the mains leads. at these. points at an equal electric high frequency difference of potential to earth and, in parallel with the said inductances, a variable condenser in series with a variable re-.

sistance, the said filter being interposed at a ,point'in the mains leads between the transformer and the receiver and the mains side of. the filter being electrically coupled by means 

